The present invention in general is directed to a pneumatic drive mechanism for positioning various types of apparatus. More specifically, the pneumatic drive mechanism is of the type having a drive housing which contains a drive element such as a diaphragm disk, a piston or the like, which is movably seated therein and which is rigidly connected to a drive rod or similar mechanism. The drive element is operated with compressed air on at least one side thereof. At least one spring is utilized to provide opposing force on the drive element to the action of the compressed air and is arranged within the drive housing. At least one signal processing device, such as a position controlller, a position encoder, a limit signal generator, a solenoid valve, or a device for converting electrical current signals to pneumatic pressure signals (hereinafter referred to as i/p converters) is also contained within the drive housing.
Pneumatic drive mechanisms of the type set forth above are used for converting the pressure of a pneumatic system into a corresponding physical movement of an apparatus. Such drives serve, for example, for the actuation of a positioning mechanism. In order to achieve a position dependent on the input pressure, the forces of pressure must be balanced against the external forces acting on the drive rod and against the spring force contained within the drive mechanism. A simple acting pneumatic drive to which the invention is especially directed has at least one drive housing, a diaphragm comprising a diaphragm disk or a piston and a drive rod, as well as, a set of springs for establishing intermediate positions of the drive rod in response to the pressure of the pneumatic system. An opposite direction of action may be achieved by reversing the entire drive mechanism as is well known in the art.
Since the external forces which act on the drive rod vary and additional movement-dependent frictional forces may be present, position controllers which allocate a defined path for the input signal in a closed control loop are frequently utilized. Dependent on the execution of the position controller, the input signal can be pneumatic or electric. The position controller is usually attached to the component part to be actuated, for example, to a control valve, being attached thereto as a separate device. However, solutions are also known wherein the position controller is mounted over the drive mechanism in the form of a "disk" or is mounted between the drive mechanism and the component part to be actuated. There are also similar arrangements for other signal processing devices, such as limit signal generators, position encoders, solenoid valves, i/p converters and other auxiliary devices.